The main goal is to study the effect of meal number, size and texture on metabolism and incretin levels after GBP. Patients will be studied before GBP (T0) and 12-15 months after GBP (T1). At T0 and T1, patients will come for 2 study days for 8 hours: On one study day, a single meal will be served, on the second study day, three small isocaloric meals, with the order of the conditions randomly assigned. The total amount of calories and the overall nutrient composition will be equivalent between conditions. The meals will be either all solid or all liquid. Patients enrolled in the study will be randomly assigned to solid or liquid test meals.